FDTD numerical simulation and application research of small-loop transient electromagnetic method in shallow water

Abstract

At present, there are no appropriate exploration methods for the shallow water geophysical surveys with depths less than 100 m. In this paper, the detection feasibility of small-loop transient electromagnetic method (TEM) in shallow water was researched from both theoretical and practical application aspects. Firstly, the propagation characteristics of the multi-turn small-loop electromagnetic field and the magnetic dipole in space were compared. Next, a homogeneous half-space shallow water model and a typical low-resistance abnormal body shallow water model were established by using the finite-difference time-domain (FDTD) method. The research results indicate that the strength of the magnetic field intensity is mainly affected by the depth of water, resistivity, and emission current. The response curve of the low-resistance abnormal body at different times indicates double-peak attenuation law. The response of low-resistance abnormal at different depths of shallow water indicates single-peak, double-peak, and peak-to-valley attenuation laws, and the response of low-resistance abnormal at different resistivity of shallow water indicates single-peak and peak-to-valley attenuation laws. The EA parameters were introduced to analyze the effects of different thicknesses and different resistivity on the response of low-resistance abnormal. Finally, the effectiveness and accuracy of the method were verified when comparing the high-density resistivity method with the results of the transient electromagnetic method on water. The research work provides a theoretical reference for the qualitative analysis of the response characteristics and data processing interpretation of the small-loop transient electromagnetic method in shallow water.